The Potential of Current- and Wind-Driven Transport for Environmental Management of the Baltic Sea

The ever increasing impact of the marine industry and transport on vulnerable sea areas puts the marine environment under exceptional pressure and calls for inspired methods for mitigating the impact of the related risks. We describe a method for preventive reduction of remote environmental risks caused by the shipping and maritime industry that are transported by surface currents and wind impact to the coasts. This method is based on characterizing systematically the damaging potential of the offshore areas in terms of potential transport to vulnerable regions of an oil spill or other pollution that has occurred in a particular area. The resulting maps of probabilities of pollution to be transported to the nearshore and the time it takes for the pollution to reach the nearshore are used to design environmentally optimized fairways for the Gulf of Finland, Baltic Proper, and south-western Baltic Se

Sea Level Change: Mapping Danish Municipality Needs for Climate Information

Climate change will affect the coastline of the Baltic Sea through changes in sea level, storm surges and waves. In Denmark, a large part of the responsibility for climate adaptation lies with the local municipalities. The purpose of this study was to map the user needs for coastal climate change information of five municipalities in the Danish south western Baltic Sea and the Danish Coastal Authority in a cost-efficient way and to transform the mapping into local climate indicators. An interview template was customized to form the basis for telephone interviews of key stakeholders and systematic gathering of the results. The interest for the interviews was high, and response from the interviewed persons on the use of the template was very positive. During the interviews, it was clear that the municipalities have access to extensive information on the population and infrastructure, as well as detailed geographical information. The main interests were in very high quality storm surge warnings and present day and future extreme sea level and wave heights. This should be based on modeling of past storm surges and future changes, taking observations, and historical records into account. There was a big need for more detailed information than presently available, and for common scenarios, which will help the collaboration between municipalities. Within this study, the user requirements were used to define targeted climate indicators. Within the C3S CODEC project, the indicators will be provided for the municipalities, based on a downscaling of European scale storm surge, and wave simulations to local scale

INTERCOMPARAISON DE MODÈLES AUTONOMES ET DE MODÈLES EMBOÎTÉS À DEUX VOIES POUR LE SERVICE EN AVAL DU CMEMS

International audiencePrediction of hydrographic conditions e.g., sea level, temperature, salinity and currents in coastal-estuary continuum is the basis for climate change adaptation and mitigation and ecosystem-based management in coastal waters. In this study, we compare and develop two strategies: either use stand-alone Limfjord setup with boundary conditions from CMEMS or extend the CMEMS Baltic Monitoring Forecasting Centre (BAL-MFC) setup with a nested Limfjord domain. The resolution of Limfjord domain in about 185 m horizontal resolution. This domain is not covered by CMEMS, despite its importance for sea shipping, aquaculture and mussel fi sheries. The ocean model that is applied is the BAL-MFC HBM model (HIROMB-BOOS Model). The results show that both approaches are able to provide high quality sea level forecast for storm surge warning, temperature, salinity and currents with reasonably good quality for ecosystem-based management both for nested an stand-alone models. The models are able to handle the shallow thermoclines in summer as well as the strong tidal and wind driven transport through narrow straits in autumn and winter. Nested models usually have better performance and do not depend on possible change of CMEMS model that supplies boundary conditions. Nevertheless, stand-alone setup is attractive as it requires much less computational resources, can be tuned more effectively, less limits for increasing the resolution

Simulating transport and distribution of marine macro-plastic in the Baltic Sea

We simulated the spatial distribution and dynamics of macro plastic in the Baltic Sea, using a new Lagrangian approach called the dynamical renormalization resampling scheme (DRRS). This approach extends the super-individual simulation technique, so the weight-per-individual is dynamic rather than fixed. The simulations were based on a mapping of the macro plastic sources along the Baltic coast line, and a five year time series of realistic wind, wave and current data to resolve time-variability in the transport and spatial distribution of macro plastics in the Baltic Sea. The model setup has been validated against beach litter observations and was able to reproduce some major spatial trends in macroplastic distributions. We also simulated plastic dispersal using Green’s functions (pollution plumes) for individual sources. e.g. rivers, and found a significant variation in the spatial range of Green’s functions corresponding to different pollution sources. We determined a significant temporal variability (up to 7 times the average) in the plastic concentration locally, which needs to be taken into account when assessing the ecological impact of marine litter. Accumulation patterns and litter wave formation were observed to be driven by an interplay between positive buoyancy, coastal boundaries and varying directions of physical forcing. Finally we determined the range of wind drag coefficients for floating plastic, where the dynamics is mostly directly wind driven, as opposed to indirectly by surface currents and waves. This study suggests that patterns of litter sorting by transport processes should be observable in many coastal and off-shore environments

Deciphering the Ages of Saline Water in the Baltic Sea by Anthropogenic Radiotracers

The slow water renewal endows the Baltic Sea a strong retention of pollutants/nutrients. Constraining water age is a practical way to depict the transport timescales for water masses and accompanying soluble substances. Although the water ages in the Baltic Sea have been resolved by 3D ocean models 20 year ago, the simulated results have not been verified. In this work, we exploited two anthropogenic radionuclides (129I and 236U) to constrain the ages of inflowing North Sea saline waters into the Baltic Sea by using the Tracer Age and Transit Time Distribution approaches. Our results indicate that the Baltic Sea has a highly stratified structure with a more diffusive bottom circulation and a more advective surface circulation. The circulation timescale for the saline water in the Baltic Sea was estimated to be &gt;30 years from the bottom of Arkona Basin to the surface of central Baltic Sea. This work demonstrates the power of anthropogenic radiotracers in investigating circulation timescale and mixing processes in the Baltic Sea and provides the first observation-based proof for the multi-decadal retention of (radioactive) pollutants within the Baltic Sea. </div